This invention relates generally to the modification of a receiver antenna pattern, and, more particularly to hardware architecture for digital beamforming that is cascadable and used as a common building block in the customization of beamforming systems.
The basis for controlling antenna patterns through the use of beamforming is well known. The primary function of a digital beamformer is to create an output that is a weighted sum of the input channels. By doing this, it is possible to accentuate certain types of signals present in the input channels, while at the same time reducing or xe2x80x9cnullingxe2x80x9d other undesirable signals as long as the signals arrive at the antenna from different directions. The beamformer receives signals at several spatially separated antennas. By controlling the weighting coefficients, an effective antenna pattern is produced which has nulls in the direction of the source of undesirable signals and a main lobe in the direction of a source of a desired signal.
As previously stated, beamforming is a process by which received signals from several different antenna elements are combined in a way that accentuates desired signals and attenuates, or reduces, undesirable signals. The method of combination involves, in general, applying an amplitude scaling and phase shift to the received signal from each antenna element, and summing these results together. This combination of signals from the antenna elements results in an effective antenna xe2x80x9cpattern.xe2x80x9d The effect of this antenna pattern is to enhance or reduce radio frequency (RF) signals arriving at the antenna array depending on the angle of arrival (AOA) of the RF signal.
The weighting coefficients for the digital beamformer must be calculated dynamically in order to properly direct the antenna pattern nulls. If the direction of the nulls and main lobe is known, the weighting coefficients could be directly calculated. However, the direction of the source of undesirable signals is typically not known. Because of this, a method is used to determine the beamformer coefficients, which is based on a covariance estimate of the input channel data. This covariance matrix is post-processed and the desired direction of the main lobe is applied. The final result is a set of beamformer coefficients. A different set of beamformer coefficients may be determined for each desired direction of the main lobe.
The weighting coefficients must also be calculated often. In the case where relative positions change rapidly, or the platform on which the digital beamformer resides is maneuvering, the directions in which to point the antenna pattern nulls and main lobe may change quickly.
Traditionally, a beamformer is custom designed to meet the specifications of a particular customer system. The beamformer includes a variable number of input channels, a variable number of output, a covariance estimator, first-in-first-out (FIFO) buffers, a weighted sum calculator, and a processor interface. Basically, no two beamformers are exactly the same because no to customers have exactly the same specifications. Therefore, each beamformer development program is unique making it costly and time consuming.
There is a wide range of potential applications from small to large. A small application may require only two input channels and one output beam. A large application may require 8 input channels and 8 output beams. The cost of the beamformer is directly proportional of the xe2x80x9cnumber of gatesxe2x80x9d contained in the device. Though one large device could be used for a small application by the non-use of input channels and/or output beams, the device may be 4 to 8 times the cost of a device that is specifically designed for the smaller application. Since smaller applications tend to be more cost sensitive, the cost may be prohibitive. Also, a large device requires more power that impacts costs and potentially imposes thermal limitations to the system components. Conversely, a small beamformers currently available are not scalable up to the large application specifications.
The present invention comprises a modular beamformer architecture made up of three primary features. The first is the creation of a data ring where data samples are circulated so that a covariance matrix may be calculated on all data pairs. The second is the ability to cascade multiple devices so that partial weighted sums may be accumulated in successive devices. The third is the ability to add multiple devices whose weighted sum calculation logic work independently but on the same input data so that different antenna patterns may be realized.
These features enable processes to be performed in xe2x80x9creal timexe2x80x9d as the RF signal arrives. Any pause in processing may result in lost data. The calculation of beamformer coefficients from the covariance matrix may be done offline by a microprocessor or digital signal processor.
An architecture for a digital beamformer is described which allows it to be broken down into smaller building blocks. These building blocks can then be connected in different ways to support different numbers of input channels and output beams.
For a better understanding of the present invention, reference is made to the accompanying drawings and detailed description and its scope will be pointed out in the appended claims.